Silicon and its compounds are important and inevitable materials in the fields of semiconductors. These materials have a wide range of applications including, for example, silicon oxide films as gate insulators for semiconductor devices, amorphous silicon films and silicon nitride films as thin-film transistors, polysilicon films for three-dimensional structural elements such as MEMS, silicon carbide (SiC) films for low-power-consumption transistors and the like. Attention is particularly given to silicon semiconductor devices under the circumstance that the high-density integration of semiconductor elements, as typified by transistors for DRAM and flash memories, has been proceeding year after year.
During semiconductor manufacturing, silicon and its compounds are commonly processed into predetermined shapes or removed by predetermined manufacturing steps e.g. final manufacturing steps. Dry etching has been conventionally widely used for such processing and removal of silicon and its compounds. In the dry etching of silicon and its compounds, fine etching performance and high etching accuracy are required. Thus, in-plane etching uniformity and etching selectivity are regarded as important factors in view of wafer upsizing, fine pattern formation etc. It is also required to improve the etching rate for high productivity.
Conventionally, plasma dry etching methods have been widely used for etching of silicon. In the plasma dry etching methods, it is common practice to utilize fluorine-containing compounds such as SF6 (sulfur hexafluoride) and C4F8 (perfluorocyclobutane) as etching gases. These etching gases are however questioned as a cause of global warming because of their very high global warming potential of several thousands to several tens of thousands. On the other hand, fluorine-containing interhalogen compounds are known as effective etching gases for etching of silicon because of their relatively low global warming potential and high reactivity against the silicon.
For example, Patent Document 1 discloses a method for anisotropic plasma etching of a silicon substrate with the use of an etching gas containing iodine fluoride as one kind of interhalogen compound.
In the conventional plasma etching methods, however, there occurs large electrical damage to samples by plasma. Concerns are thus rising that, in the case of plasma etching silicon on complicated shaped semiconductor elements, etching-resistant parts such as dielectric parts of the semiconductor elements may also become damaged.
As a solution to such a problem, researches have been made on methods for etching silicon and its compounds by so-called plasma-less etching treatment without the need for plasma excitation.
For example, Patent Document 2 discloses a method for processing a surface of a sample by plasma-less etching treatment without causing electrical or ultraviolet damage to the sample. In the plasma-less etching treatment, the sample surface is etched by generating reactive gas clusters upon abrupt adiabatic expansion of an etching gas due to a pressure difference between gas supply pipe pressure (primary pressure) and chamber inside pressure (secondary pressure), and then, ejecting the reactive gas clusters to the sample surface.
Patent Document 3 discloses a method for etching a silicon layer by plasma-less etching treatment with the use of a fluorine-containing interhalogen compound such as BrF3, ClF3 or XeF2. It is described in this patent document that the etching selectivity of the silicon layer against metal or metal silicon can be improved with the addition of an inert gas such as nitrogen and argon to the interhalogen compound.
Patent Document 4 discloses a method for production of iodine heptafluoride (hereinafter sometimes referred to as “IF7”). It is described in this patent document that iodine heptafluoride is usable as an etching gas. Further, Patent Document 5 discloses the use of a fluorine-containing interhalogen compound for etching of an oxide or semiconductor material.
There are however no reports that actually use iodine heptafluoride for etching applications and discuss the conditions of etching with iodine heptafluoride.